Noun

1 the process whereby heat changes something from
a solid to a liquid; "the power failure caused a refrigerator melt
that was a disaster"; "the thawing of a frozen turkey takes several
hours" [syn: thaw, melt, melting]

English

Verb

Melting is a process that results in the phase
change of a substance from a solid to a liquid. The internal energy of a
solid substance is increased (typically by the application of heat)
to a specific temperature (called the melting
point) at which it changes to the liquid phase. An object that
has melted completely is molten.

The melting point of a substance is a
characteristic property. The melting point may not be equal to the
freezing
point. This is evident in the phenomenon known as supercooling. In the case
of water, ice crystals typically require a seed on which to begin
formation. Water on a very clean glass surface will often supercool
several degrees below the melting point without freezing. Fine
emulsions of pure water have been cooled to -38 degrees celsius
without the nucleation of ice taking place. For this reason,
melting point is a characteristic property of a substance while
freezing point is not.

Molecular vibrations

When the internal energy of a gas is
increased by the application of an external energy source, the
molecular vibrations of the substance increases. As these
vibrations increase, the substance becomes more and more ordered.
Fusion is also another term used for this.

Constant temperature

Substances melt at a constant
temperature, the melting
point. Further increases in temperature (even with continued
application of energy) do not occur until the substance is
molten.

The thermodynamics of melting

From a thermodynamics point
of view, at the melting point the change in Gibbs
free energy (\Delta G) of the Material is zero, because the
enthalpy (H) and the
entropy (S) of the
material are increasing (\Delta H, \Delta S > 0). Melting
phenomenon happens when the Gibbs free energy of the liquid becomes
lower than the solid for that material. At various pressures this
happens at a specific temperature. It can also be shown that:

\Delta S = \frac

The "T","\Delta S", and "\Delta H" in the above
are respectively the temperature at the melting point, change of
entropy of melting, and the change of enthalpy of melting.